The present invention relates to razors.
As referred to in this disclosure, a "razor" is defined as a self-contained shaving unit having at least one blade, a blade support, a guard surface attached to the blade support and extending outwardly from the support below the blade or blades, and a cap covering and protecting the blade or blades. The support and cap combine to maintain the blade or blades in a predetermined shaving position. The razor can include a disposable handle to provide a disposable razor per se or it may be in the form of a disposable cartridge for use with a permanent handle. In both instances the disposable cartridge and the razor head of the disposable razor are substantially identical.
The blades utilized in modern shaving razors incorporate a plurality of features which coact to provide efficient and comfortable shaving action. A shaving razor blade is far sharper than an ordinary industrial razor blade or knife. Sharpness can be expressed and measured in terms of the "ultimate tip radius". Shaving razor blades ordinarily have ultimate tip radii of about 600 Angstroms or less, whereas industrial razor blades, cutting knives and the like ordinarily have ultimate tip radii of several thousand Angstroms. Moreover, modern shaving razor blades have lubricant coatings, such as coatings of fluorocarbon polymers on their cutting edges. The lubricant decreases the frictional forces created by engagement of the blade with the individual whiskers, and hence materially reduces the drag or "pull" experienced by the user upon shaving.
To be considered satisfactory by modern standards, a shaving razor blade should remain usable for many shaves. The blade should retain a keen edge and should retain its lubricant during these repeated shaves, despite exposure to the physical effects of contact with the beard and skin, and despite exposure to the chemical effects of water, soaps and the like encountered in the shaving environment. The shaving razor blade must be adapted for efficient and economical mass production. It must withstand shipment, storage and handling under ordinary conditions without special care. All of these factors together create a formidable technical challenge.
Typical modern shaving razor blades incorporate a substrate of stainless steel, such as an iron and chromium-containing martensitic stainless steel, together with a hard coating of chromium or chromium nitride overlying the stainless steel substrate at least along the cutting edge of the blade. A coating of a fluoropolymer lubricant such as polytetrafluoroethylene overlies the hard coating and adheres thereto. The hard coating may be on the order of a few hundred Angstroms thick.
The hard coating is applied by a process known as sputtering. As further discussed hereinbelow, sputtering ordinarily is conducted under a controlled atmosphere, typically a noble gas at extremely low pressures. Following the sputtering process, the semifinished blades, with the hard coating thereon, are removed from the controlled atmosphere. The blades are coated with the lubricant by applying a dispersion of the fluorocarbon polymer in a fugitive liquid solvent, evaporating off the solvent and then fusing the remaining lubricant by heating to above the melting point of the polymer. Although the fusing step typically is conducted in an inert atmosphere, the blades are exposed to ordinary room air during application of the lubricant dispersion, and during any storage period between application of the hard coating and application of the lubricant dispersion.
Razors incorporating blades according to this general construction have been regarded heretofore as superior in that they provide a good combination of shaving performance, durability and low cost. Nonetheless, there have been needs for still further improvements.
One avenue of research in the razor art has been directed toward the development of a hard coating which could be used as a substitute for chromium in the blade. Ordinary cutting tools become dull and unusable due to gradual abrasive wear of their cutting edges. Resistance to this type of wear typically is related directly to hardness. There are many materials harder than chromium. In theory, any such hard material might be a candidate for experimentation. However, shaving razor blade cutting edges normally do not become dull due to this type of wear. The very sharp, thin edges of shaving razor blades normally become dull due to microscopic fractures of the edge. Therefore, hardness alone does not always correlate well with blade edge durability in a shaving razor blade. Wear resistance results achieved in other applications may not reliably predict blade edge durability in a shaving razor blade. Moreover, a hard coating for use in a shaving razor blade must be compatible with the lubricant coating and with the processes used to apply the lubricant. In particular, the lubricant must adhereto the hard coating to provide a durable lubricating effect in use. Adhesion between hard coating materials and lubricants is not predictable. Many otherwise suitable hard coating materials are incompatible with lubricants in that the lubricant will not adhere satisfactorily. For these and other reasons, the search for better hard coatings for use in shaving razor blades has not been successful heretofore.